It is desirable for a manufacturer to offer a wide-range of static lift pressures and air volumes for a line of industrial or commercial vacuum cleaning machines. These machines are rated in terms of the static lift and air volumes (in cubic feet per minute, for example), which are developed by the machine. The price of the machine, of course, increases with higher static lift and air volume ratings. The ratings of static lift and air volumes are related to the size and capacity of the vacuum motor as well as the number of stages in the fan assembly driven by the motor.
Typically, the motor is mounted in a housing and the entire housing and motor (sometimes referred to as the "vacuum power head") may be removed from the canister to empty the canister. It is thus desirable to mount different size motors in housings of the same exterior dimensions. Vacuum motors differ in diameter (i.e., circumference) and axial dimension, the motors having the larger capacities also being greater in size.
In the past, arrangements have been made to mount motors of the same circumference but different axial dimensions in a single housing by using annular seating gaskets of different depth so that the total axial dimension of the motor and gasket remain constant. Compensating for differences in the axial dimension of the fan housing of the vacuum motors through gaskets of different axial dimensions is not always desirable because the axial dimension of the gasket must be larger as the axial dimension of the vacuum chamber is smaller. With larger gaskets, for longer periods of use, the sealing ability of the gasket diminishes; and the ability of the motor to continue to generate the rated static lift diminishes as air leaks begin to form around the gasket.
Moreover, compensating for differences in axial dimension of the motor with gaskets does not permit the interchangeability of the vacuum chambers of different diameters. Current commercial technique does not permit the interchangeability of different numbers or configurations of motors having different diameters in the same housing, as does the present invention.